P54/WGI-14 - Changes to the underlying scientific-technical assessment to ensure consistency with the approved SPM These trickle backs will be implemented in the Chapter during copy-editing

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(1)P54/WGI-14 - Changes to the underlying scientific-technical assessment to ensure consistency with the approved SPM These trickle backs will be implemented in the Chapter during copy-editing Chapter/Su pp. Material. Chapter Page:Line. TS. 7:4. 10:27. TS. 16:7. 10:28. TS. 16:14. 4:12. TS. 20:7. Replace "climate system" with "atmosphere, ocean, and land components of the climate system.". Box SPM.1.1. TS. 21:9. Add "illustrative" before "scenarios", to read "A core set of five illustrative scenarios …". Box SPM.1.1. TS. 22:11. Add "illustrative" before "scenarios", to read "A core set of five illustrative scenarios …". SPM Page:Line. B5.2 Footnote 22. Summary of edit to be made. In the definition of Low likelihood, high impact outcomes, the beginning of the sentence now starting with "Events…" should be changed to "Outcomes/events whose probability…" Replace sentence starting on line 7 with "Developments in the latest generation" and ending on line 10 with "and many other aspects across the Earth system" with: "This report assesses results from climate models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) of the World Climate Research Programme. These models include new and better representation of physical, chemical and biological processes, as well as higher resolution, compared to climate models considered in previous IPCC assessment reports. This has improved the simulation of the recent mean state of most large-scale indicators of climate change and many other aspects across the climate system. Some differences from observations remain, for example in regional precipitation patterns." Replace sentence on lines 14-15 "While past warming is well simulated by the new generation of models, some individual models simulate past surface warming that is either below or above that observed." with "The CMIP6 historical simulations assessed in this report have an ensemble mean global surface temperature change within 0.2°C of the observations over most of the historical period, and observed warming is within the very likely range of the CMIP6 ensemble. However, some CMIP6 models simulate a warming that is either above or below the assessed very likely range of observed warming". Replace text from line 11-15 "In this report, a core set of five scenarios is used to explore climate change over the 21st century and beyond (Section TS.2). They are labelled SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP58.514, and span a wide range of radiative forcing levels in 2100. Scenarios in AR6 cover a broader range of emissions futures than considered in AR5, including high CO2 emissions scenarios without climate change mitigation as well as a low CO2 emissions scenario reaching net zero CO2 emissions (see Core Concepts Box) around mid-century." with the following text: Box SPM.1.1. TS. 22:11-15. 4:25-4:29. TS. 27:52. 4:25-4:29. TS. 28:24. 19:23. TS. 30:4. 12:23. TS. 30:22. 6 August 2021. "Scenarios in AR6 cover a broader range of emissions futures than considered in AR5, including high CO2 emissions scenarios without climate change mitigation as well as a low CO2 emissions scenario reaching net zero CO2 emissions (see Core Concepts Box) around mid-century. In this report, a core set of five illustrative scenarios is used to explore climate change over the 21st century and beyond (Section TS.2). They are labelled SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5, and span a wide range of radiative forcing levels in 2100. They start in 2015, and include scenarios with high and very high GHG emissions (SSP3-7.0 and SSP5-8.5) and CO2 emissions that roughly double from current levels by 2100 and 2050, respectively, scenarios with intermediate GHG emissions (SSP2-4.5) and CO2 emissions remaining around current levels until the middle of the century, and scenarios with very low and low GHG emissions and CO2 emissions declining to net zero around or after 2050, followed by varying levels of net negative CO2 emissions (SSP1-1.9 and SSP1-2.6). " after the first 'increased by', add the words '0.99 [0.84-1.10] C from 1850-1900 to the first two decades of the 21st century (2001-2020), and' (then continue with the existing sentence). Add after first comma (between 1850-1900 to 1995-2014 and 1850-1900 to 2011-2020): between 1850-1900 and the first two decades of the 21st century by 0.99 [0.84-1.20]C, Add following sentence after "very likely range of CMIP6 trends.": "Furthermore, the heating of the climate system continued during this period, as reflected in the continued warming of the global ocean (very high confidence ) and in the continued rise of hot extremes over land (medium confidence )". Rephrase comparison to SR1.5 so as to connect more effectively to the SPM. Replace "about 10 years earlier than the midpoint” with “in the early part”. Page 1.

(2) P54/WGI-14 - Changes to the underlying scientific-technical assessment to ensure consistency with the approved SPM These trickle backs will be implemented in the Chapter during copy-editing SPM Page:Line. Chapter/Su pp. Material. Chapter Page:Line. 12:23. TS. 30:24. 12:27. TS. 30:26. 5:17. TS. 32:Table. 4:12. TS. 32:2. 4:12. TS. 32:13. 22:33. TS. 39:52-54. 5:17. TS. 40:38. 6:45-48. TS. 40:38. 6:45-48. TS. 41:51-53. 5:17. TS. 44:26. B.4.2, 24, 16. TS. 47:35. 8: 48-51. TS. 55:19. Rephrase comparison to SR1.5 so as to connect more effectively to the SPM. Replace "the ten-year” with “this”. Add sentence referring to another location in the SR1.5. After "(medium confidence)", add: “When considering scenarios similar to SSP1-1.9 instead of linear extrapolation, the SR1.5 estimate of when 1.5°C global warming is crossed is close to the central estimate reported here.“ Last row of Table TS.1: Change 1970 to 1971 Replace "climate system as a whole" with "atmosphere, ocean, and land components of the climate system, taken together, " Replace "climate system" with "atmosphere, ocean, and land". Before "weather patterns and water patterns", add "regional" ; at the end of end of the sentence, before the full stop and LOS, add ", and drying in Europe". So the full sentence should read: "If an AMOC collapse were to occur, it would very likely cause abrupt shifts in the regional weather patterns and water cycle, such as a southward shift in the tropical rain belt, and could result in weakening of the African and Asian monsoons and strengthening of Southern Hemisphere monsoons, and drying in Europe." Change "ocean acidification" to "surface open ocean acidification" Add after '(virtually certain).' as follows: A long-term increase in surface open ocean pH occurred over the past 50 million years (high confidence), and surface ocean pH as low as recent times is uncommon in the last 2 million years (medium confidence) Replace sentence starting 'There is very high confidfence that present-day surface pH' with: A longterm increase in surface open ocean pH occurred over the past 50 million years (high confidence), and surface ocean pH as low as recent times is uncommon in the last 2 million years (medium confidence) Change 1970 to 1971 to support confidence statement added to SPM, please add the following sentence after the one which finishes …declining atmospheric CO2 concentrrations. "Under SSP1-1.9 models project combined land and ocean sinks turn into a weak source by 2100 (medium confidence)." Replace “435 [325 to 545]” with “282 [177 to 387]”.. 8: 48-51. TS. 55:20. Replace “1971-2018” with “1971-2006”.. 8: 48-51. TS. 56:1. Replace “1971-2018” with “1971-2006”.. 8: 48-51. TS. 56:2. Replace “0.57 [0.43 to 0.72]” with “0.50 [0.32 to 0.69]”.. Figure SPM.3. TS Box TS.10, fig 1. 137. this figure should be replaced with the accepted figure SPM3. 6 August 2021. Summary of edit to be made. Page 2.

(3) AR6 WGI Report – List of corrigenda to be implemented The corrigenda listed below will be implemented in the TS during copy-editing.. TECHNICAL SUMMARY Document (Chapter, Annex, Supp. Mat…) TS. Section. Title page. Page :Line (based on the final pdf FGD version) 1:44. TS TS. Introduction 5:1 Introduction 5:3. TS. TS1.2.2. 16 :33. TS TS TS TS TS. TS1.2.2 TS1.2.2 TS1.3.2 TS1.2.2 Figure TS.4. 17 : 14 18 :16 25 :41 16 :33 21 :42. TS. Figure TS.5 25 :10. TS. Figure TS.6 26 :40. TS. CSB TS1. 27:52 – 27:54. Detailed info on correction to make. TS Review Editors were mistakenly missed off the cover page. Please add: "Review Editors: Valérie Masson-Delmotte (France), Greg Flato (Canada), Noureddine Yassa (Algeria)" Add “http://interactive-atlas.ipcc.ch” as a footnote to “Atlas”. Insert “It comprises a regional information component which supports many of the chapters of the Report and a regional synthesis component which supports the Technical Summary and Summary for Policymakers.” after “information.” remove 6.2.1.2 (does not exist) and 6.3.6 callouts and replace with 6.2.2, 6.4.5, 6.4, The order of references should be changes to 6.4, 7.4.2, FAQ 7.2 Change {3.6.1, 3.6.2} to {3.6} remove reference 8.4.3 add reference to 2.8.2 and FAQ 3.3 in the {} Please add as first sentence to the figure caption: The intent of this figure is to illustrate the process-chain starting from emissions up to the changes in the climate system and in climatic impactdrivers Please add as first sentence to the figure caption: The intent of this figure is to show how scenarios are linked to Global Warming Levels, and to provide examples of the evolution of patterns of change with GWL. Please add as first sentence to the figure caption: The intent is for this figure to summarise many different aspects of the Technical Summary related to observed and projected changes in global temperature and associated regional changes in climatic impact drivers relevant for impact and risk assessment. Replace ‘, and the 52 last decade was more likely than not warmer than any multi-centennial period after the Last Interglacial, 53 roughly 125,000 years ago.’ By ‘. Temperatures as high as during the most recent decade (2011–-2020) exceed the warmest centennial-scale range reconstructed for the present interglacial, around 6,500 years ago [0.2°C to –-1°C] (medium confidence). The next most recent warm period was about 125,00 years ago during the last interglacial when the multi-centennial temperature range [0.5°C to 1.5°C] encompasses the 2011-2020 values (medium confidence).’ Reason: Consistency with SPM edits to HS2.2. 1.

(4) TS. TS CrossSectional Box TS.1. 27:54 To 28:1. Replace: "The likely range of human-induced change in global surface temperature in 2010–201916 relative to 1850– 1900 is 1.07 [0.8 to 1.3] °C, encompassing the observed warming for that period of 1.06 [0.88 to 1.21] °C, while change attributable to natural forcing is only –0.1 to +0.1°C. " with "The likely range of human-induced change in global surface temperature in 2010–2019 relative to 1850–1900 is 0.8°C–1.3°C, with a central estimate of 1.07°C, encompassing the best estimate of observed warming for that period, which is 1.06°C with a very likely range of 0.88°C, to 1.21°C, while the likely range of the change attributable to natural forcing is only –0.1°C to +0.1°C.". TS. CSB TS1. 27:52 – 27:54. Replace ‘, and the last decade was more likely than not warmer than any multi-centennial period after the Last Interglacial, roughly 125,000 years ago.’ By ‘Temperatures as high as during the most recent decade (2011–-2020) exceed the warmest centennial-scale range reconstructed for the present interglacial, around 6,500 years ago [0.2°C to –-1°C] (medium confidence). The next most recent warm period was about 125,00 years ago during the last interglacial when the multi-centennial temperature range [0.5°C to 1.5°C] encompasses the 2011-2020 values (medium confidence).’ Reason: Consistency with SPM edits to HS2.2. TS. CSB TS1. 28:41. Replace ‘in at least the last two thousand years (medium confidence), confidence), and it is more likely than not that no multi-centennial period after the Last Interglacial (roughly 125,000 years ago) was warmer globally than the most recent decade’ By ‘in at least the last two thousand years (high confidence). Temperatures as high as during the most recent decade (2011–-2020) exceed the warmest centennial-scale range reconstructed for the present interglacial, around 6,500 years ago [0.2°C to –-1°C] (medium confidence). The next most recent warm period was about 125,00 years ago during the last interglacial when the multi-centennial temperature range [0.5°C to -1.5°C] encompasses the 2011-2020 values (medium confidence).’ Reason: Consistency with SPM edits to HS2.2. TS TS. CSB1 TS CrossSectional Box TS.1. 28 :15 29:44-46. Salmon text: adding a reference to {4.5} Replace: "The likely range of human-induced change in global surface temperature in 2010–201916 relative to 1850– 1900 is 1.07 [0.8 to 1.3] °C (Figure CrossSection Box TS.1, Figure 1), encompassing the observed warming for that period of 1.06 [0.88 to 1.21] °C, while change attributable to natural forcing is only –0.1 to +0.1°C. " with "The likely range of human-induced change in global surface temperature in 2010–2019 relative to 1850–1900 is 0.8°C–1.3°C, with a central estimate of 1.07°C (Figure Cross-Section Box TS.1, Figure 1), encompassing the best estimate of observed warming for that period, which is 1.06°C with a very likely range of 0.88°C, to 1.21°C, while the likely range of the change attributable to natural forcing is only –0.1°C to +0.1°C." 2.

(5) TS. Figure TS.7 32 :19. TS. Figure TS.8 33 :18. TS. Table TS.2. Page 34, agricultural and ecological drought entry. Please add as first sentence to the figure caption: The intent of the figure is to compare the observed and simulated changes over the historical period for a range of variables are regions, with and without anthropogenic forcings, for attribution. Please add as first sentence to the figure caption: The intent of this figure is to show how future emissions choices impact key iconic large-scale indicators and to highlight that our collective choices matter. Replace label : Agricultural and ecological droughts: Intensity and/or duration With Agricultural and ecological droughts: Intensity and/or frequency. TS. Table TS.2. Page 34, agricultural and ecological drought entry. Replace for predominant fraction of land area “ With“ in some regions. “observed” and “attributed” columns Page 34, agricultural and ecological drought entry. Replace:“ for predominant fraction of land area With in more regions compared to observed changes. TS. Table TS.2. “+1.5°C” column Page 34, agricultural and ecological drought entry. TS. Table TS.2. TS. Table TS.2. TS. “+4°C” column Figure TS.9 35 :45. “+2°C” column Page 34, agricultural and ecological drought entry. TS. Figure TS.10. 37 :33. TS. Box TS.3, Figure 1. 40 :17. TS TS TS. TS2.4 TS2.5 Figure TS.11. 40 :47 40 :48 42 :19. Replace: for predominant fraction of land area With in more regions compared to 1.5°C of global warming. Replace: for predominant fraction of land area “ With in more regions compared to 2°C of global warming Please add as first sentence to the figure caption: The intent of the figure is to show the changes of the main drivers of climate system over the industrial period, with changes exceptional in a long-term context. Please add as first sentence to the figure caption: The intent of the figure is to visualize upper air temperature and circulation changes, similarity between observed and projected changes. Please add as first sentence to the figure caption: The intent of this figure is to illustrate high warming storylines compared to the CMIP6 multi-model-mean. Salmon text {} replace {4.3} with {4.3.2} Salmon text {} remove 9.4 and 9.6 Please add as first sentence to the figure caption: The intent of the figure is to show that observed projected time series of many ocean and cryosphere indicators are consistent. 3.

(6) TS. Box TS.4. 44 :35. TS. Box TS.4. 45 :2. TS. Box TS.4. 45 :19. TS. Box TS.4, Figure 1. 45 :49. TS. Box TS.4, Figure 1. 45 :49. TS TS. Box TS5 Box TS.5, Figure 1. 46 :31 48 :3. TS. Section TS2.6. 49:5-7. TS. Section TS2.6. 49:7-8. TS. Figure TS.12. 50 :10. TS. Box TS.6, Figure 1. 51 : 53. TS. infographic. 53-54. TS. TS.3.1. 55: 20. By 2100, GMSL is projected to rise by 0.28–0.55 m (likely range) under SSP1- 1.9 and 0.63–1.01 m (likely range) under SSP5-8.5 relative to the 1995–2014 average (medium confidence). By 2100, the projected rise is between 0.38 m (0.28–0.55 m, likely range) (SSP1-1.9) and 0.77 m (0.63–1.01 m, likely range) (SSP5-8.5) (Table 9.9). By 2150, considering only those processes in whose projections we have at least medium confidence and assuming no acceleration in ice-mass flux after 2100, GMSL is projected to rise between 0.6 m (0.4–0.9 m, likely range) (SSP1-1.9) and 1.3 m (1.0–1.9 m, likely range) (SSP5-8.5), relative to the period 1995–2014 based on the SSP scenario extensions. Please add as first sentence to the figure caption: The intent of the figure is to: 1) show the century-scale GMSL projections in the context of the 20th century observations; 2) illustrate “deep uncertainty” in projections by considering the timing of GMSL rise milestones; 3) show the long-term commitment associated with different warming levels, including the paleo evidence to support this. Box TS.4, Figure 1: is missing callouts. Please add the following to the end of the figure caption: "{4.3.2, 9.6.1, 9.6.2, 9.6.3, Box 9.4}." Salmon text {} add reference to FAQ 5.1 Please add as first sentence to the figure caption: The intent of the figure is to show the response of the carbon cycle to CO2 emissions and climate and its role in determining future CO2 levels through projected changes to sinks and sink fractions. Replace:“ The majority of the land area has experienced decreases in available water during dry seasons due to the overall increase in evapotranspiration (medium confidence).“ With“ Human-induced climate change has contributed to increases in agricultural and ecological droughts in some regions due to increases in evapotranspiration (medium confidence)“ Replace:“ The land area affected by increasing drought frequency and severity will expand with increasing global warming (high confidence; Figure TS.12c).“ With“ More regions are affected by increases in agricultural and ecological droughts with increasing global warming (high confidence; see also Figure TS.12c) “ Please add as first sentence to the figure caption: The intent of this figure is to show that extremes and mean land variables change consistently with warming levels.To show the changes with global warming levels of water cycle indicators (i.e. precipitation and runoff) over tropical and extratropical land in terms of mean and interannual variability (interannual variability increases at a faster rate than the mean) Please add as first sentence to the figure caption: The intent of the figure is to give a geographical overview of changes in multiple components of the global water cycle using an intermediate emission scenario. Important key message: without drastic reductions in GHG emissions, human- induced global warming will be associated with widespread changes in all components of the water cycle. Please add as first sentence to the figure caption: The intent of the figure is to show possible climate futures. The climate change that people will experience this century and beyond depends on our greenhouse gases emissions, how much global warming this will cause and the response of the climate system to this warming. Replace “153 [100 to 206]” with “152 [100 to 205]” (change needed for revised numbers in Ch7) 4.

(7) TS. TS.3.1. 55: 22. TS TS. TS.3.1 TS3.1. 55:22 56:51. TS. TS3.2.1. 58:33. TS. TS.3.2.1. 59:18. TS TS. TS3.2.2 Box TS9. 61:15 71 :22. TS TS. Box TS12 Box TS.12, Figure 1. 76 :50 77 :27. TS. TS4.3. 85:33. TS. TS.4.3. 86:2. TS. Figure TS.18. TS. TS4.3 and Figure TS.22 TS.4.3.2.2 TS.4.3.2.2 4.3.2.6 4.3.2.7 4.3.2.7 Figure TS.23. 87:18-19 and 145:18-19. Figure TS.24. 88 :25. TS TS TS TS TS TS. TS. 96:6 96:8 96:33 97:12 97:21 87 :48. Replace “Earth system heating” with “Earth energy imbalance” (previous terminology removed for FGD). Replace “rate of global energy” by “annual rate of global energy”. Replace “1.21 [0.90 to 1.51]” by “1.19 [0.81 to 1.58]” and replace “0.33 [0.25 to 0.41]” by “0.35 [0.16 to 0.54]” Replace “These higher mean ECS and TCR values can, in some models, be traced to changes in extratropical cloud feedbacks (medium confidence).” with “These higher mean ECS and TCR values can be traced to a positive net cloud feedback that is larger in CMIP6 by about 20%.” Add a sentence after “The TCRE falls likely in the 1.0°C–2.3°C per 1000 PgC range, with a best estimate of 1.65°C per 1000 PgC.”: “This is equivalent to a 0.27°C–0.63°C range with a best estimate of 0.45 °C when expressed in units per 1000 GtCO2.” Replace “ECS” by “ECS (equilibrium climate sensitivity)” Salmon text {} remove the ref to {TS3.3.2} + harmonise reference to TS (i.e. not in {} but in ()) Salmon text {} remove the reference to {10.6.4} Please add as first sentence to the figure caption: The intent of the figure is to provide an example of different lines of evidence used to provide an assessment of the confidence in or likelihood of a projected change in regional climate and which of these lines of evidence are available to view and explore in the Interactive Atlas. Insert “The Regional Synthesis component of the Interactive Atlas provides comprehensive synthesis information about changes in all of the individual Climatic Impact-Drivers (CIDs) across all of the AR6 WG I reference regions.” after “(CIDs).” In Table TS.5, add arrow (to indicate past upward trend) and “ ** ” in the cell corresponding to Small Islands – Pacific – Extreme Heat, to indicate medium confidence in attribution of observed changes Change sentence: “Coloured areas show the Chapter 4 assessed very likely range of global surface temperature projections and thick coloured central lines the median estimate, for each respective scenario, relative to the original scenario emissions.” to the following sentence: “Coloured areas show the Chapter 4 assessed very likely range of global surface temperature projections and thick coloured central lines the median estimate, for each respective scenario. These temperature projections are expressed relative to cumulative CO2 emissions that are available for emission-driven CMIP6 ScenarioMIP experiments for each respective scenario.” Insert “and can be visualised in the Regional Synthesis component of the Interactive Atlas” after “Table TS.5” and delete “[Placeholder: This summary is also represented visually in the Interactive Atlas.]” Replace “the assessment” with “some assessment” Delete “+TIB” Replace “very likely” by “likely” Replace “Cross-Chapter Box Atlas.1” with “Cross-Chapter Box Atlas.2” Replace “Cross-Chapter Box Atlas.1” with “Cross-Chapter Box Atlas.2” Please add as first sentence to the figure caption: The intent of the figure is to show for the WG I AR6 reference regions when a signal of annual mean surface temperature change emerged from the noise of interannual variability in two global datasets and thus also provide some information on observational uncertainty. Please add as first sentence to the figure caption: The intent of the figure is to show that there is a consistent message about 5.

(8) TS. TS TS. TS TS TS TS TS TS. TS. Section TS4.3. 87:26. the patterns of projected change in extreme daily temperatures from the CMIP5, CMIP6 and CORDEX ensembles. Add line of line which was omitted in the FGD: {11.9, 12.4, Atlas.1}. TS.4.3 Table TS.5 TS.4.3 Table TS.5. 86:2. TS.4.3 TS4.3.2.9 Box TS.4, Figure 1 caption Figure TS.15. 97:11 98 :22 121:22. Currently TS sections in {} should be displayed in (), e.g., (Table TS.5, Figure TS.25). In Table TS.5 Please change color for A&E droughts from light purple to white for Pacific Islands Please remove footnote 5; change footnote index “6” into “5” in both table and footnote text below; change footnote index “7” into “6” in both table and footone text below; (table should be consistent with Table 12.9) replace the "Small" with "Caribbean" and remove "Islands" Salmon text {} add reference to {12.3.6} Lightly shaded thick/thin bars show 17th–83rd/5th–95th percentile. 129. Figure has been updated and uploaded on the Figure Manager. 131:7 137 :4. Replace “ECS” by “ECS (equilibrium climate sensitivity)” Please add as first sentence to the figure caption: The intent of the figure is to show that climate change is already affecting every region across the globe with many observed changes in extremes attributable to human activity. Please add as first sentence to the figure caption: The intent of the figure is to show that while changes in climatic impactdrivers will happen everywhere, there is a specific combination of changes in each region will experience.. Box TS.10, Figure 1 Figure TS.22. 86:2. 145 :5. 6.

(9) Final Government Distribution. IPCC AR6 WGI. TS. Technical Summary Coordinating Authors: Paola A. Arias (Colombia), Nicolas Bellouin (United Kingdom/France), Erika Coppola (Italy), Richard G. Jones (United Kingdom), Gerhard Krinner (France/Germany, France), Jochem Marotzke (Germany), Vaishali Naik (United States of America), Matthew D. Palmer (United Kingdom), Gian-Kasper Plattner (Switzerland), Joeri Rogelj (United Kingdom /Belgium), Maisa Rojas (Chile), Jana Sillmann (Norway/Germany), Trude Storelvmo (Norway), Peter W. Thorne (Ireland/ United Kingdom), Blair Trewin (Australia). AC BJ C EC E P T TE TO D FI VE N R AL S I ED ON IT IN G. Authors: Krishna Achuta Rao (India), Bhupesh Adhikary (Nepal), Richard P. Allan (United Kingdom), Kyle Armour (United States of America), Govindasamy Bala (India/ United States of America), Rondrotiana Barimalala (South Africa/Madagascar), Sophie Berger (France/Belgium), Josep G. Canadell (Australia), Christophe Cassou (France), Annalisa Cherchi (Italy), William Collins (United Kingdom), William D. Collins (United States of America), Sarah L. Connors (France/ United Kingdom), Susanna Corti (Italy), Faye Cruz (Philippines), Frank J. Dentener (EU/The Netherlands), Claudine Dereczynski (Brazil), Alejandro Di Luca (Australia, Canada/Argentina), Aida Diongue Niang (Senegal), Francisco J. Doblas-Reyes (Spain), Alessandro Dosio (Italy), Hervé Douville (France), François Engelbrecht (South Africa), Veronika Eyring (Germany), Erich Fischer (Switzerland), Piers Forster (United Kingdom), Baylor Fox-Kemper (United States of America), Jan S. Fuglestvedt (Norway), John C. Fyfe (Canada), Nathan P. Gillett (Canada), Leah Goldfarb (France/ United States of America), Irina Gorodetskaya (Portugal/Russian Federation, Belgium), Jose Manuel Gutierrez (Spain), Rafiq Hamdi (Belgium), Ed Hawkins (United Kingdom), Helene T. Hewitt (United Kingdom), Pandora Hope (Australia), Akm Saiful Islam (Bangladesh), Christopher Jones (United Kingdom), Darrell S. Kaufman (United States of America), Robert E. Kopp (United States of America), Yu Kosaka (Japan), James Kossin (United States of America), Svitlana Krakovska (Ukraine), June-Yi Lee (Republic of Korea), Jian Li (China), Thorsten Mauritsen (Sweden, Denmark), Thomas K. Maycock (United States of America), Malte Meinshausen (Australia/Germany), Seung-Ki Min (Republic of Korea), Pedro M. S. Monteiro (South Africa), Thanh Ngo-Duc (Vietnam), Friederike Otto (United Kingdom /Germany), Izidine Pinto (South Africa/Mozambique), Anna Pirani (Italy/ United Kingdom, Italy), Krishnan Raghavan (India), Roshanka Ranasinghe (The Netherlands/Sri Lanka,Australia), Alex C. Ruane (United States of America), Lucas Ruiz (Argentina), Jean-Baptiste Sallée (France), Bjørn H. Samset (Norway), Shubha Sathyendranath (UK/Canada, United Kingdom, Overseas Citizen of India), Sonia I. Seneviratne (Switzerland), Anna A. Sörensson (Argentina), Sophie Szopa (France), Izuru Takayabu (Japan), Anne-Marie Treguier (France), Bart van den Hurk (The Netherlands), Robert Vautard (France), Karina von Schuckmann (France/Germany), Sönke Zaehle (Germany), Xuebin Zhang (Canada), Kirsten Zickfeld (Canada/Germany) Contributing Authors: Guðfinna Aðalgeirsdóttir (Iceland), Lincoln M. Alves (Brazil), Terje Berntsen (Norway), Sara M. Blichner (Norway), Lisa Bock (Germany), Gregory G. Garner (United States of America), Joelle Gergis (Australia), Sergey K. Gulev (Russian Federation), Mathias Hauser (Switzerland), Flavio Lehner (United States of America/Switzerland), Chao Li (China), Marianne T. Lund (Norway), Daniel J. Lunt (United Kingdom), Sebastian Milinski (Germany), Gemma Teresa Narisma (Philippines), Zebedee R. J. Nicholls (Australia), Dirk Notz (Germany), Sophie Nowicki (USA/France, USA), Bette Otto-Bliesner (USA), Brodie Pearson (United States of America / United Kingdom), Adam S. Phillips (United States of America), Lucas Ruiz (Argentina), Stéphane Sénési (France), Lucas Silva (Portugal/Switzerland), Aimee B. A. Slangen (The Netherlands), Thomas F. Stocker (Switzerland), Claudia Tebaldi (United States of America), Sabin Thazhe Purayil (India), Andrew Turner (United Kingdom), Steven Turnock (United Kingdom), Carolina Vera (Argentina), Cunde Xiao (China), Panmao Zhai (China). SU. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54. Technical Summary. Review Editors. Valérie Masson-Delmotte (France), Gregory M. Flato (Canada), Noureddine Yassa (Algeria). TS-1. Total pages: 150.

(10) Final Government Distribution. IPCC AR6 WGI. AC BJ C EC E P T TE TO D FI VE N R AL S I ED ON IT IN G. This Technical Summary should be cited as: Arias, P. A., N. Bellouin, E. Coppola, R. G. Jones, G. Krinner, J. Marotzke, V. Naik, M. D. Palmer, G-K. Plattner, J. Rogelj, M. Rojas, J. Sillmann, T. Storelvmo, P. W. Thorne, B. Trewin, K. Achuta Rao, B. Adhikary, R. P. Allan, K. Armour, G. Bala, R. Barimalala, S. Berger, J. G. Canadell, C. Cassou, A. Cherchi, W. Collins, W. D. Collins, S. L. Connors, S. Corti, F. Cruz, F. J. Dentener, C. Dereczynski, A. Di Luca, A. Diongue Niang, F. J. Doblas-Reyes, A. Dosio, H. Douville, F. Engelbrecht, V. Eyring, E. Fischer, P. Forster, B. Fox-Kemper, J. S. Fuglestvedt, J. C. Fyfe, N. P. Gillett, L. Goldfarb, I. Gorodetskaya, J. M. Gutierrez, R. Hamdi, E. Hawkins, H. T. Hewitt, P. Hope, A. S. Islam, C. Jones, D. S. Kaufman, R. E. Kopp, Y. Kosaka, J. Kossin, S. Krakovska, J-Y. Lee, J. Li, T. Mauritsen, T. K. Maycock, M. Meinshausen, S-K. Min, P. M. S. Monteiro, T. Ngo-Duc, F. Otto, I. Pinto, A. Pirani, K. Raghavan, R. Ranasinghe, A. C. Ruane, L. Ruiz, J-B. Sallée, B. H. Samset, S. Sathyendranath, S. I. Seneviratne, A. A. Sörensson, S. Szopa, I. Takayabu, A-M. Treguier, B. van den Hurk, R. Vautard, K. von Schuckmann, S. Zaehle, X. Zhang, K. Zickfeld, 2021, Technical Summary. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu and B. Zhou (eds.)]. Cambridge University Press. In Press.. Date: August 2021. This document is subject to copy-editing, corrigenda and trickle backs.. SU. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24. Technical Summary. TS-1 bis. Total pages: 150.

(11) Final Government Distribution. 1. Technical Summary. IPCC AR6 WGI. Table of Content. 2 3. Introduction ..................................................................................................................................................... 4. 4. Box TS.1:. 5. TS.1. Core Concepts Central to This Report .................................................................................. 5. A Changing Climate .......................................................................................................................... 11. 6. TS.1.1. 7. Box TS.2:. 8. TS.1.2. Context of a Changing Climate ........................................................................................... 11 Paleoclimate ........................................................................................................................... 12 Progress in Climate Science ................................................................................................ 15. TS.1.2.1. Observation-based products and their assessments ............................................................. 15. 10. TS.1.2.2. Climate Model Performance ................................................................................................ 16. TS.1.2.3. Understanding Climate Variability and Emerging Changes................................................ 18. TS.1.2.4. Understanding of Human Influence..................................................................................... 20. 11 12 13 14 15 16. AC BJ C EC E P T TE TO D FI VE N R AL S I ED ON IT IN G. 9. TS.1.3. Assessing Future Climate Change ....................................................................................... 20. TS.1.3.1. Climate Change Scenarios ................................................................................................... 21. TS.1.3.2. Global Warming Levels and Cumulative CO2 Emissions ................................................... 23. TS.1.4. From Global to Regional Climate Information for Impact and Risk Assessment ............... 25. 17. Cross-Section Box TS.1: Global Surface Temperature Change ............................................................... 27. 18. TS.2. Large-scale Climate Change: Mean Climate, Variability and Extremes ..................................... 31. 19. TS.2.1. Changes Across the Global Climate System ....................................................................... 31. 20. TS.2.2. Changes in the Drivers of the Climate System .................................................................... 35. 21. TS.2.3. Upper Air Temperatures and Atmospheric Circulation....................................................... 37. 22. Box TS.3:. 23. TS.2.4. The Ocean ............................................................................................................................ 40. 24. TS.2.5. The Cryosphere.................................................................................................................... 42. 25. Box TS.4:. Sea Level ................................................................................................................................. 44. 26. Box TS.5:. The Carbon Cycle .................................................................................................................. 46. 27. TS.2.6. 28. Box TS.6:. 29. Infographic TS.1: Climate Futures. ............................................................................................................. 52. 30. TS.3. Low-Likelihood, High-Warming Storylines ........................................................................ 38. Land Climate, Including Biosphere and Extremes .............................................................. 48. Water Cycle ............................................................................................................................ 50. Understanding the Climate System Response and Implications for Limiting Global Warming 55. 31. TS.3.1. Radiative Forcing and Energy Budget ................................................................................. 55. 32. TS.3.2. Climate Sensitivity and Earth-System Feedbacks ............................................................... 57. TS.3.2.1. Equilibrium Climate Sensitivity, Transient Climate Response, and Transient Climate Response to Cumulative Carbon-dioxide Emissions............................................................. 57. 36. SU. 33 34. 37. TS.3.3.1. Remaining Carbon Budgets and Temperature Stabilization................................................ 61. 38. TS.3.3.2. Carbon Dioxide Removal .................................................................................................... 64. 39. TS.3.3.3. Relating Different Forcing Agents ...................................................................................... 66. 35. 40. TS.3.2.2. TS.3.3. Box TS.7:. Earth System Feedbacks ...................................................................................................... 59 Temperature Stabilization, Net Zero Emissions and Mitigation ......................................... 61. Climate and Air Quality Responses to Short-lived Climate Forcers in Shared. Do Not Cite, Quote or Distribute. TS-2. Total pages: 150.

(12) Final Government Distribution. 1. Technical Summary. IPCC AR6 WGI. Socioeconomic Pathways ....................................................................................................... 68. 2. Box TS.8:. Earth System Response to Solar Radiation Modification .................................................. 69. 3. Box TS.9:. Irreversibility, Tipping Points and Abrupt Changes ......................................................... 71. 4. TS.4. 5 6 7 8. Regional Climate Change ................................................................................................................. 72. TS.4.1. Generation and Communication of Regional Climate Change Information ....................... 72. TS.4.1.1 Box TS.10:. Sources and Methodologies for Generating Regional Climate Information ....................... 73 Event Attribution................................................................................................................... 73. TS.4.1.2. Regional Climate Information Distillation and Climate Services ....................................... 75. Box TS.11:. Climate Services ..................................................................................................................... 76. 10 11. Box TS.12: Atlas. Multiple Lines of Evidence for Assessing Regional Climate Change and the Interactive 76. 12. TS.4.2. 13 14 15. AC BJ C EC E P T TE TO D FI VE N R AL S I ED ON IT IN G. 9. TS.4.2.1. Regional Fingerprints of Anthropogenic and Natural Forcing ............................................ 78. TS.4.2.2. Modes of Variability and Regional Teleconnections .......................................................... 78. TS.4.2.3. Interplay Between Drivers of Climate Variability and Change at Regional Scales ............ 81. 16. Box TS.13:. 17 18. TS.4.3 Drivers. 19 20 21 22 23 24 25 26 27 28 29 30. Drivers of Regional Climate Variability and Change.......................................................... 77. Monsoons ................................................................................................................................ 83 Regional Climate Change and Implications for Climate Extremes and Climatic Impact85. TS.4.3.1. Common Regional Changes in Climatic Impact-Drivers .................................................... 87. TS.4.3.2. Region-by-Region Changes in Climatic Impact-Drivers..................................................... 89. TS.4.3.2.1. Africa ............................................................................................................................... 90. TS.4.3.2.2. Asia .................................................................................................................................. 91. TS.4.3.2.3. Australasia ....................................................................................................................... 93. TS.4.3.2.4. Central and South America .............................................................................................. 94. TS.4.3.2.5. Europe.............................................................................................................................. 95. TS.4.3.2.6. North America ................................................................................................................. 95. TS.4.3.2.7. Small Islands.................................................................................................................... 96. TS.4.3.2.8. Polar ................................................................................................................................. 97. TS.4.3.2.9. Ocean ............................................................................................................................... 98. TS.4.3.2.10. Other Typological Domains ............................................................................................ 99. Box TS.14:. 32. Figures .......................................................................................................................................................... 101. 33 34. Urban Areas ........................................................................................................................... 99. SU. 31. Do Not Cite, Quote or Distribute. TS-3. Total pages: 150.

(13) Final Government Distribution. IPCC AR6 WGI. Introduction The Working Group I (WGI) contribution to the Intergovernmental Panel on Climate Change Sixth Assessment Report (AR6) assess the physical science basis of climate change. As part of that contribution, this Technical Summary (TS) is designed to bridge between the comprehensive assessment of the WGI Chapters and its Summary for Policymakers (SPM). It is primarily built from the Executive Summaries of the individual chapters and atlas and provides a synthesis of key findings based on multiple lines of evidence (e.g., analyses of observations, models, paleoclimate information and understanding of physical, chemical and biological processes and components of the climate system). All the findings and figures here are supported by and traceable to the underlying chapters, with relevant chapter sections indicated in curly brackets.. AC BJ C EC E P T TE TO D FI VE N R AL S I ED ON IT IN G. Throughout this Technical Summary, key assessment findings are reported using the IPCC calibrated uncertainty language (Chapter 1, Box 1.1). Two calibrated approaches are used to communicate the degree of certainty in key findings, which are based on author teams’ evaluations of underlying scientific understanding:. (1) Confidence1 is a qualitative measure of the validity of a finding, based on the type, amount, quality and consistency of evidence (e.g., data, mechanistic understanding, theory, models, expert judgment) and the degree of agreement; and (2) Likelihood2 provides a quantified measure of confidence in a finding expressed probabilistically (e.g., based on statistical analysis of observations or model results, or both, and expert judgement by the author team or from a formal quantitative survey of expert views, or both).. Where there is sufficient scientific confidence, findings can also be formulated as statements of fact without uncertainty qualifiers. Throughout IPCC reports, the calibrated language is clearly identified by being typeset in italics.. The context and progress in climate science (TS.1) is followed by a Cross-Section Box TS.1 on global surface temperature change. TS.2 provides information about past and future large-scale changes in all components of the climate system. TS.3 summarises knowledge and understanding of climate forcings, feedbacks and responses. Infographic TS.1 uses a storyline approach to integrate findings on possible climate futures. Finally, TS.4 provides a synthesis of climate information at regional scales.3 The list of acronyms used in the WGI Report is in Annex VIII. The AR6 WGI report promotes best practices in traceability and reproducibility, including through adoption of the Findable, Accessible, Interoperable, and Reusable (FAIR) principles for scientific data. Each chapter has a data table (in its Supplementary Material) documenting the input data and code used to generate its figures and tables. In addition, a collection of data and code from the report has been made freely-available online via long-term archives. ([URL to access WGI data to be added by 30 June]). 1. In this Technical Summary, the following summary terms are used to describe the available evidence: limited, medium, or robust; and for the degree of agreement: low, medium, or high. A level of confidence is expressed using five qualifiers: very low, low, medium, high, and very high, and typeset in italics, e.g., medium confidence. For a given evidence and agreement statement, different confidence levels can be assigned, but increasing levels of evidence and degrees of agreement are correlated with increasing confidence (see Chapter 1, Box 1.1 for more details).. SU. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41. Technical Summary. 2. In this Technical Summary, the following terms have been used to indicate the assessed likelihood of an outcome or a result: virtually certain 99– 100% probability, very likely 90–100%, likely 66–100%, about as likely as not 33–66%, unlikely 0–33%, very unlikely 0–10%, exceptionally unlikely 0–1%. Additional terms (extremely likely: 95–100%, more likely than not >50–100%, and extremely unlikely 0–5%) may also be used when appropriate. Assessed likelihood is typeset in italics, e.g., very likely (see Chapter 1, Box 1.1 for more details). Throughout the WGI report and unless stated otherwise, uncertainty is quantified using 90% uncertainty intervals. The 90% uncertainty interval, reported in square brackets [x to y], is estimated to have a 90% likelihood of covering the value that is being estimated. The range encompasses the median value, and there is an estimated 10% combined likelihood of the value being below the lower end of the range (x) and above its upper end (y). Often the distribution will be considered symmetric about the corresponding best estimate, but this is not always the case. In this report, an assessed 90% uncertainty interval is referred to as a ‘very likely range’. Similarly, an assessed 66% uncertainty interval is referred to as a ‘likely range’. 3. The regional trackback matrices that provide the location of the assessment findings synthesized in TS.4 are in the Supplementary Material (SM) for Chapter 10.. Do Not Cite, Quote or Distribute. TS-4. Total pages: 150.

(14) Final Government Distribution. IPCC AR6 WGI. These FAIR principles are central to the WGI Interactive Atlas, an online tool that complements the WGI Report by providing flexible spatial and temporal analyses of past, observed and projected climate change information. ([URL to access WGI data to be added by 30 June]). Regarding the representation of robustness and uncertainty in maps, the method chosen for the AR64 differs from the method used in the Sixth Assessment Report (AR5). This choice is based on new research in the visualization of uncertainty and on user surveys.. [START BOX TS.1 HERE] Box TS.1: Core Concepts Central to This Report. AC BJ C EC E P T TE TO D FI VE N R AL S I ED ON IT IN G. This box provides short descriptions of key concepts which are relevant to the AR6 WGI assessment, with a focus on their use in the Technical Summary and the Summary for Policymakers. The Glossary (Annex VII) includes more information on these concepts along with definitions of many other important terms and concepts used in this Report. Characteristics of Climate Change Assessment. Global warming: Global warming refers to the change of global surface temperature relative to a baseline depending upon the application. Specific global warming levels, such as 1.5°C, 2°C, 3°C or 4°C, are defined as changes in global surface temperature relative to the years 1850–1900 as the baseline (the earliest period of reliable observations with sufficient geographic coverage). They are used to assess and communicate information about global and regional changes, linking to scenarios and used as a common basis for WGII and WGIII assessments. (TS.1.3, Cross-Section Box TS.1) {1.4.1, 1.6.2, 4.6.1, Cross-Chapter Boxes 1.5, 2.3, 11.1, and 12.1, Atlas.3-Atlas.11, Glossary} Emergence: Emergence refers to the experience or appearance of novel conditions of a particular climate variable in a given region. This concept is often expressed as the ratio of the change in a climate variable relative to the amplitude of natural variations of that variable (often termed a ‘signal-to-noise’ ratio, with emergence occurring at a defined threshold of this ratio). Emergence can be expressed in terms of a time or a global warming level at which the novel conditions appear and can be estimated using observations or model simulations. (TS.1.2.3, TS.4.2) {1.4.2, FAQ 1.2, 7.5.5, 10.3, 10.4, 12.5.2, Cross-Chapter Box Atlas.1, Glossary}. Cumulative carbon dioxide (CO2) emissions: The total net amount of CO2 emitted into the atmosphere as a result of human activities. Given the nearly linear relationship between cumulative CO 2 emissions and increases in global surface temperature, cumulative CO2 emissions are relevant for understanding how past and future CO2 emissions affect global surface temperature. A related term – remaining carbon budget – is used to describe the total net amount of CO2 that could be released in the future by human activities while keeping global warming to a specific global warming level, such as 1.5°C, taking into account the warming contribution from non-CO2 forcers as well. The remaining carbon budget is expressed from a recent specified date, while the total carbon budget is expressed starting from the pre-industrial period. (TS.1.3, TS.3.4) {1.6.3, 5.5, Glossary}. SU. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50. Technical Summary. Net zero CO2 emissions: A condition that occurs when the amount of CO2 emitted into the atmosphere by human activities equals the amount of CO2 removed from the atmosphere by human activities over a specified period of time. Net negative CO2 emissions occur when anthropogenic removals exceed anthropogenic emissions. (TS.3.3) {Box 1.4, Glossary} 4. The AR6 figures follow either one of the following approaches. For observations, the absence of ‘x’ symbols shows areas with statistical significance (while the presence of ‘x’ indicates non-significance). For model projections, the method offers two approaches with varying complexity. In the simple approach, high agreement (≥80%) is indicated with no overlay, and diagonal lines (///) shows low agreement (<80%); In the advanced approach, areas with no overlay display robust signal (≥66% of models show change greater than the variability threshold and ≥80% of all models agree on the sign of change), reverse diagonal lines (\\\) shows no robust signal, and crossed lines show conflicting signals (i.e., significant change but low agreement). Cross-Chapter Box Atlas.1 provides more information on the AR6 method for visualizing robustness and uncertainty on maps.. Do Not Cite, Quote or Distribute. TS-5. Total pages: 150.

(15) Final Government Distribution. IPCC AR6 WGI. Human Influence on the Climate System Earth’s energy imbalance: In a stable climate, the amount of energy that the Earth receives from the Sun is approximately in balance with the amount of energy that is lost to space in the form of reflected sunlight and thermal radiation. ‘Climate drivers’, such as an increase in greenhouse gases or aerosols, interfere with this balance, causing the system to either gain or lose energy. The strength of a climate driver is quantified by its effective radiative forcing (ERF), measured in W m-2. Positive ERF leads to warming and negative ERF leads to cooling. That warming or cooling in turn can change the energy imbalance through many positive (amplifying) or negative (dampening) climate feedbacks. (TS.2.2, TS.3.1, TS.3.2) {2.2.8, 7.2, 7.3, 7.4, Box 7.1, Box 7.2, Glossary}. AC BJ C EC E P T TE TO D FI VE N R AL S I ED ON IT IN G. Attribution: Attribution is the process of evaluating the relative contributions of multiple causal factors to an observed change in climate variables (e.g., global surface temperature, global mean sea level change), or to the occurrence of extreme weather or climate-related events. Attributed causal factors include human activities (such as increases in greenhouse gas concentration and aerosols, or land-use change) or natural external drivers (solar and volcanic influences), and in some cases internal variability. (TS.1.2.4, TS.2, Box TS.10) {CrossWorking Group Box: Attribution, 3.5, 3.8, 10.4, 11.2.4, Glossary} Committed change, long-term commitment: Changes in the climate system, resulting from past, present and future human activities, which will continue long into the future (centuries to millennia) even with strong reductions in greenhouse gas emissions. Some aspects of the climate system, including the terrestrial biosphere, deep ocean and the cryosphere, respond much more slowly than surface temperatures to changes in greenhouse gas concentrations. As a result, there are already substantial committed changes associated with past greenhouse gas emissions. For example, global mean sea level will continue to rise for thousands of years, even if future CO2 emissions are reduced to net zero and global warming halted, as excess energy due to past emissions continues to propagate into the deep ocean and as glaciers and ice sheets continue to melt. (TS.2.1, Box TS.4, Box TS.9) {1.2.1, 1.3, Box 1.2, Cross-Chapter Box 5.3} Climate Information for Regional Climate Change and Risk Assessment. Distillation: The process of synthesizing information about climate change from multiple lines of evidence obtained from a variety of sources, taking into account user context and values. It leads to an increase in the usability, usefulness, and relevance of climate information, enhances stakeholder trust, and expands the foundation of evidence used in climate services. It is particularly relevant in the context of co-producing regional-scale climate information to support decision-making. (TS.4.1, Box TS.11) {10.1, 10.5, 12.6}. (Climate change) risk: The concept of risk is a key aspect of how the IPCC assesses and communicates to decision-makers about the potential for adverse consequences for human or ecological systems, recognising the diversity of values and objectives associated with such systems. In the context of climate change, risks can arise from potential impacts of climate change as well as human responses to climate change. WGI contributes to the common IPCC risk framing through the assessment of relevant climate information, including climatic impact-drivers and low-likelihood, high impact outcomes. (TS.1.4, TS.4.1, Box TS.4) {Cross-Chapter Boxes 1.3 and 12.1, Glossary}. Climatic impact-drivers: Physical climate system conditions (e.g., means, events, extremes) that can be directly connected with having impacts on human or ecological systems are described as ‘climatic impactdrivers’ (CIDs) without anticipating whether their impacts are detrimental (i.e., as for hazards in the context of climate change risks) or provide potential opportunities. A range of indices may capture the sector- or application-relevant characteristics of a climatic impact-driver and can reflect exceedances of identified tolerance thresholds. (TS.1.4, TS.4.3) {12.1-12.3, FAQ12.1, Glossary}. SU. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55. Technical Summary. Storylines: The term storyline is used both in connection to scenarios (related to a future trajectory of emissions or socio-economic developments) or to describe plausible trajectories of weather and climate conditions or events, especially those related to high levels of risk. Physical climate storylines are introduced in AR6 to explore uncertainties in climate change and natural climate variability, to develop and communicate integrated Do Not Cite, Quote or Distribute. TS-6. Total pages: 150.

(16) Final Government Distribution. IPCC AR6 WGI. and context-relevant regional climate information, and to address issues with deep uncertainty5, including lowlikelihood, high-impact outcomes. (TS.1.4, Box TS.3, Infographic TS.1) {1.4.4, Box 10.2, Glossary} Low-likelihood, high impact outcomes: Events whose probability of occurrence is low or not well known (as in the context of deep uncertainty) but whose potential impacts on society and ecosystems could be high. To better inform risk assessment and decision-making, such low-likelihood outcomes are considered if they are associated with very large consequences and may therefore constitute material risks, even though those consequences do not necessarily represent the most likely outcome. (TS.1.4, Box TS.3, Figure TS.6) {1.4.4, 4.8, Cross Chapter Box 1.3, Glossary}. AC BJ C EC E P T TE TO D FI VE N R AL S I ED ON IT IN G. [END BOX TS.1 HERE]. As part of the AR6 cycle, the IPCC produced three Special Reports in 2018 and 2019: the Special Report on Global Warming of 1.5°C (SR1.5), the Special Report on Oceans and Cryosphere in a Changing Climate (SROCC), and the Special Report on Climate Change and Land (SRCCL).. The AR6 WGI Report provides a full and comprehensive assessment of the physical science basis of climate change that builds on the previous assessments and these Special Reports and consider new information and knowledge from the recent scientific literature6, including longer observational datasets, new scenarios and model results.. The structure of the AR6 WGI report is designed to enhance the visibility of knowledge developments and to facilitate the integration of multiple lines of evidence, thereby improving confidence in findings. The Report has been peer-reviewed by the scientific community and governments (Annex X provides the Expert Reviewer list). The substantive introduction provided by Chapter 1 is followed by a first set of chapters dedicated to large-scale climate knowledge (Chapters 2–4), which encompasses observations and paleoclimate evidence, causes of observed changes, and projections, and are complemented by Chapter 11 for large-scale changes in extremes. The second set of chapters (Chapters 5–9) is orientated around the understanding of key climate system components and processes, including the global cycles of carbon, energy and water; short-lived climate forcers and their link to air quality; the ocean, cryosphere and sea level change. The last set of chapters (Chapters 10–12 and the Atlas) is dedicated to the assessment and distillation of regional climate information from multiple lines of evidence at sub-continental to local scales (including urban climate), with a focus on recent and projected regional changes in mean climate, extremes, and climatic impact-drivers. The new online Interactive Atlas allows users to interact in a flexible manner through maps, time series and summary statistics with climate information for a set of updated WGI reference regions. The Report also includes 34 Frequently Asked Questions and answers for the general public. [URL to access FAQs to be added by 30 June] Together, this Technical Summary and the underlying chapters aim at providing a comprehensive picture of knowledge progress since the WGI AR5. Multiple lines of scientific evidence confirm that the climate is changing due to human influence. Important advances in the ability to understand past, present, and possible future changes should result in better-informed decision-making. Some of the new results and main updates to key findings in AR6 WGI compared to AR5, SR1.5, SRCCL, and SROCC are summarized below. Relevant Technical Summary sections with further details are shown in. SU. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46. Technical Summary. Although not a core concept of the WGI Report, deep uncertainty is used in the Technical Summary in the following sense: ‘A situation of deep uncertainty exists when experts or stakeholders do not know or cannot agree on: (1) appropriate conceptual models that describe relationships among key driving forces in a system; (2) the probability distributions used to represent uncertainty about key variables and parameters; and/or (3) how to weigh and value desirable alternative outcomes’ (Lempert et al., 2003). Lempert, R. J., Popper, S. W., and Bankes, S. C. (2003). Shaping the next one hundred years: New methods for quantitative long-term strategy analysis (MR-1626-RPC). Santa Monica, CA: The RAND Pardee Center. 5. 6. The assessment covers scientific literature accepted for publication by 31 January 2021.. Do Not Cite, Quote or Distribute. TS-7. Total pages: 150.

(17) Final Government Distribution. IPCC AR6 WGI. parenthesis after each bullet point. Selected Updates and/or New Results since AR5 Human influence7 on the climate system is now an established fact: The Fourth Assessment Report (AR4) stated in 2007 that ‘warming of the climate system is unequivocal’, and the AR5 stated in 2013 that ‘human influence on the climate system is clear’. Combined evidence from across the climate system strengthens this finding. It is unequivocal that the increase of CO2, methane (CH4) and nitrous oxide (N2O) in the atmosphere over the industrial era is the result of human activities and that human influence is the principal driver of many changes observed across the atmosphere, ocean, cryosphere and biosphere. (TS.1.2, TS.2.1) ● Observed global warming to date: A combination of improved observational records and a series of very warm years since AR5 have resulted in a substantial increase in the estimated level of global warming to date. The contribution of changes in observational understanding alone between AR5 and AR6 leads to an increase of about 0.1°C in the estimated warming since 1850–1900. For the decade 2011–2020, the increase in global surface temperature since 1850–1900 is assessed to be 1.09 [0.95 to 1.20] °C.8 Estimates of crossing times of global warming levels and estimates of remaining carbon budgets are updated accordingly. (TS.1.2, Cross-Section Box TS.1) ● Paleoclimate evidence: The AR5 assessed that many of the changes observed since the 1950s are unprecedented over decades to millennia. Updated paleoclimate evidence strengthens this assessment; over the past several decades, key indicators of the climate system are increasingly at levels unseen in centuries to millennia and are changing at rates unprecedented in at least the last 2000 years. (Box TS.2, TS.2) ● Updated assessment of recent warming: The AR5 reported a smaller rate of increase in global mean surface temperature over the period 1998–2012 than the rate calculated since 1951. Based on updated observational datasets showing a larger trend over 1998–2012 than earlier estimates, there is now high confidence that the observed 1998–2012 global surface temperature trend is consistent with ensembles of climate model simulations, and there is now very high confidence that the slower rate of global surface temperature increase observed over this period was a temporary event induced by internal and naturally forced variability that partly offset the anthropogenic surface warming trend over this period, while heat uptake continued to increase in the ocean. Since 2012, strong warming has been observed, with the past five years (2016–2020) being the hottest five-year period in the instrumental record since at least 1850 (high confidence). (TS.1.2, Cross-Section Box TS.1) ● Magnitude of climate system response: In this Report, it has been possible to reduce the longstanding uncertainty ranges for metrics that quantify the response of the climate system to radiative forcing, such as the equilibrium climate sensitivity (ECS) and the transient climate response (TCR), due to substantial advances (e.g., a 50% reduction in the uncertainty range of cloud feedbacks) and improved integration of multiple lines of evidence, including paleoclimate information. Improved quantification of effective radiative forcing, the climate system radiative response, and the observed energy increase in the Earth system over the past five decades demonstrate improved consistency between independent estimates of climate drivers, the combined climate feedbacks, and the observed energy increase relative to AR5. (TS.3.2) ● Improved constraints on projections of future climate change: For the first time in an IPCC report, the assessed future change in global surface temperature is consistently constructed by combining scenario-based projections (which the AR5 focused on) with observational constraints based on past simulations of warming as well as the updated assessment of ECS and TCR. In addition, initialized forecasts have been used for the period 2019–2018. The inclusion of these lines of evidence reduces the assessed uncertainty for each scenario. (TS.1.3, Cross-Section Box TS.1). AC BJ C EC E P T TE TO D FI VE N R AL S I ED ON IT IN G. ●. SU. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48. Technical Summary. 7. Human influence on the climate system refers to human-driven activities that lead to changes in the climate system due to perturbations of the Earth’s energy budget (also called anthropogenic forcing). Human influence results from emissions of greenhouse gases, aerosols and tropospheric ozone precursors, ozone-depleting substances, and land-use change. 8 Throughout the WGI report and unless stated otherwise, uncertainty is quantified using 90% uncertainty intervals. The 90% uncertainty interval, reported in square brackets [x to y], is estimated to have a 90% likelihood of covering the value that is being estimated. The range encompasses the median value and there is an estimated 10% combined likelihood of the value being below the lower end of the range (x) and above its upper end (y). Often the distribution will be considered symmetric about the corresponding best estimate, but this is not always the case. In this report, an assessed 90% uncertainty interval is referred to as a ‘very likely range’. Similarly, an assessed 66% uncertainty interval is referred to as a ‘likely range’. Do Not Cite, Quote or Distribute. TS-8. Total pages: 150.

(18) Final Government Distribution. ●. ●. Air quality: The AR5 assessed that projections of air quality are driven primarily by precursor emissions, including methane. New scenarios explore a diversity of future options in air pollution management. The AR6 WGI reports rapid recent shifts in the geographical distribution of some of these precursor emissions, confirms the AR5 finding, and shows higher warming effects of shortlived climate forcers in scenarios with the highest air pollution. (TS.1.3, TS.2.2, Box TS.7) Effects of short-lived climate forcers on global warming: The AR5 assessed the radiative forcing for emitted compounds. The AR6 has extended this by assessing the emission-based effective radiative forcings (ERFs) also accounting for aerosol–cloud interactions. The best estimates of ERF attributed to sulphur dioxide (SO2) and CH4 emissions are substantially greater than in AR5, while that of black carbon is substantially reduced. The magnitude of uncertainty in the ERF due to black carbon emissions has also been reduced relative to AR5. Global water cycle: The AR5 assessed that anthropogenic influences have likely affected the global water cycle since 1960. The dedicated chapter in the AR6 WGI (Chapter 8) concludes with high confidence that human-caused climate change has driven detectable changes in the global water cycle since the mid-20th century, with a better understanding of the response to aerosol and greenhouse gas changes. The AR6 WGI further projects with high confidence an increase in the variability of the water cycle in most regions of the world and under all emissions scenarios (Box TS.6) Extreme events: The AR5 assessed that human influence had been detected in changes in some climate extremes. A dedicated chapter in the AR6 (Chapter 11) concludes that it is now an established fact that human-induced greenhouse gas emissions have led to an increased frequency and/or intensity of some weather and climate extremes since 1850, in particular for temperature extremes. Evidence of observed changes and attribution to human influence has strengthened for several types of extremes since AR5, in particular for extreme precipitation, droughts, tropical cyclones and compound extremes (including fire weather). (TS.1.2, TS.2.1). AC BJ C EC E P T TE TO D FI VE N R AL S I ED ON IT IN G. ●. IPCC AR6 WGI. ●. Selected Updates and/or New Results Since AR5 and SR1.5 ●. ●. ●. Timing of crossing 1.5°C global warming: Slightly different approaches are used in SR1.5 and in this Report. SR1.5 assessed a likely range of 2030 to 2052 for reaching a global warming level of 1.5°C (for a 30-year period), assuming a continued, constant rate of warming. In AR6, combining the larger estimate of global warming to date and the assessed climate response to all considered scenarios, the central estimate of crossing 1.5°C of global warming (for a 20-year period) occurs in the early 2030s, ten years earlier than the midpoint of the likely range assessed in the SR1.5, assuming no major volcanic eruption. (TS.1.3, Cross-Section Box TS.1) Remaining carbon budgets: The AR5 had assessed the transient climate response to cumulative emissions of CO2 to be likely in the range of 0.8°C to 2.5°C per 1000 GtC (1 GtC = 1 PgC = 3.667 GtCO2), and this was also used in SR1.5. The assessment in AR6, based on multiple lines of evidence, leads to a narrower likely range of 1.0°C–2.3°C per 1000 GtC. This has been incorporated in updated estimates of remaining carbon budgets (see TS.3.3.1), together with methodological improvements and recent observations. (TS.1.3, TS.3.3) Effect of short-lived climate forcers on global warming in coming decades: The SR1.5 stated that reductions in emissions of cooling aerosols partially offset greenhouse gas mitigation effects for two to three decades in pathways limiting global warming to 1.5°C. The AR6 assessment updates the AR5 assessment of the net cooling effect of aerosols and confirms that changes in short-lived climate forcers will very likely cause further warming in the next two decades across all scenarios (TS.1.3, Box TS.7) COVID-19: Temporary emission reductions in 2020 associated with COVID-19 containment led to small and positive net radiative effect (warming influence). However, global and regional climate responses to this forcing are undetectable above internal climate variability due to the temporary nature of emission reductions. (TS.3.3). SU. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55. Technical Summary. ●. Selected Updates and/or New Results Since AR5, SRCCL and SROCC ●. Atmospheric concentration of methane: SRCCL reported a resumption of atmospheric methane. Do Not Cite, Quote or Distribute. TS-9. Total pages: 150.

(19) Final Government Distribution. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31. ●. IPCC AR6 WGI. concentration growth since 2007. WGI AR6 reports a faster growth over 2014–2019 and assesses growth since 2007 to be largely driven by emissions from the fossil fuels and agriculture (dominated by livestock) sectors. (TS.2.2) Land and ocean carbon sinks: SRCCL assessed that the persistence of the land carbon sink is uncertain due to climate change. WGI AR6 finds that land and ocean carbon sinks are projected to continue to grow until 2100 with increasing atmospheric concentrations of CO2, but the fraction of emissions taken up by land and ocean is expected to decline as the CO2 concentration increases, with a much larger uncertainty range for the land sink. AR5, SR1.5 and SRCCL assessed carbon dioxide removal options and scenarios. WGI AR6 finds that the carbon cycle response is asymmetric for pulse emissions or removals, which means that CO2 emissions would be more effective at raising atmospheric CO2 than CO2 removals are at lowering atmospheric CO2. (TS.3.3, Box TS.5) Ocean stratification increase9: Refined analyses of available observations in the AR6 lead to a reassessment of the rate of increase of the global stratification in the upper 200 m to be double that estimated in SROCC from 1970 to 2018. (TS.2.4) Projected ocean oxygen loss: Future subsurface oxygen decline in new projections assessed in WGI AR6 is substantially greater in 2080–2099 than assessed in SROCC. (TS.2.4) Ice loss from glaciers and ice sheets: since SROCC, globally resolved glacier changes have improved estimates of glacier mass loss over the past 20 years, and estimates of the Greenland and Antarctic Ice Sheet loss have been extended to 2020. (TS.2.5) Observed global mean sea level change: new observation-based estimates published since SROCC lead to an assessed sea level rise estimate from 1901 to 2018 that is now consistent with the sum of individual components and consistent with closure of the global energy budget. (Box TS.4) Projected global mean sea level change: AR6 projections of global mean sea level are based on projections from ocean thermal expansion and land ice contribution estimates, which are consistent with the assessed equilibrium climate sensitivity and assessed changes in global surface temperature. They are underpinned by new land ice model intercomparisons and consideration of processes associated with low confidence to characterise the deep uncertainty in future ice loss from Antarctica. AR6 projections based on new models and methods are broadly consistent with SROCC findings. (Box TS.4). AC BJ C EC E P T TE TO D FI VE N R AL S I ED ON IT IN G. ●. Technical Summary. ● ● ●. SU. ●. 9. Increased stratification reduces the vertical exchange of heat, salinity, oxygen, carbon, and nutrients. Stratification is an important indicator for ocean circulation.. Do Not Cite, Quote or Distribute. TS-10. Total pages: 150.